US 6,867,078 B1Granted

Method for forming a microwave field effect transistor with high operating voltage

AssigneeFreescale Semiconductor, Inc.

InventorsBruce M. Green, Olin L. Hartin, Lawrence S. Klingbeil, Ellen Y. Lan, Hsin-Hua P. Li, Charles E. Weitzel

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Abstract

A microwave field effect transistor (10) has a high conductivity gate (44) overlying a double heterojunction structure (14, 18, 22) that has an undoped channel layer (18). The heterojunction structure overlies a substrate (12). A recess layer that is a not intentionally doped (NID) layer (24) overlies the heterojunction structure and is formed with a predetermined thickness that minimizes impact ionization effects at an interface of a drain contact of source/drain ohmic contacts (30) and permits significantly higher voltage operation than previous step gate transistors. Another recess layer (26) is used to define a gate dimension. A Schottky gate opening (42) is formed within a step gate opening (40) to create a step gate structure. A channel layer (18) material of InxGa1−xAs is used to provide a region of electron confinement with improved transport characteristics that result in higher frequency of operation, higher power density and improved power-added efficiency.

Claims30

Dependent claims

A method of forming a microwave field effect transistor comprising:

providing a substrate;
providing a heterojunction structure overlying the substrate, wherein the heterojunction structure includes an undoped channel layer with at least one selected from the group consisting of a material layer above, a material layer below, and a material layer above and below the undoped channel layer, the undoped channel layer having a bandgap less than a bandgap of each material layer;
providing a not intentionally doped (NED) layer overlying the heterojunction structure;
providing a heavily doped semiconductor layer overlying the NID layer;
forming a first recess within the heavily doped semiconductor layer, the first recess extending from a source region to a drain region of the microwave field effect transistor;
providing a step gate dielectric overlying the NID layer within the first recess;
providing an interlevel dielectric layer overlying the step gate dielectric;
forming source/drain (S/D) ohmic contacts respectively overlying the source region and the drain region;
forming a top dielectric layer overlying the interlevel dielectric layer and the S/D ohmic contacts;
forming a step gate opening in the top dielectric layer and the interlevel dielectric layer within the first recess between the source region and the drain region;
forming a Schottky gate opening within the step gate opening, the Schottky gate opening extending through the step gate dielectric layer and the NID layer;
providing a barrier metal layer overlying a portion of the heterojunction structure and sidewalls of the NID layer and step gate dielectric within the Schottky gate opening, the barrier metal layer further overlying the step gate dielectric, the NID layer, a portion of the heterojunction structure, and sidewalls of interlevel dielectric and top dielectric within the step gate opening;
and
providing a gate metal overlying the barrier metal layer within the Schottky gate opening and within the step gate opening.

11 more elements

A method of forming a microwave field effect transistor comprising:

providing a substrate;
providing a heterojunction structure overlying the substrate, wherein the heterojunction structure includes an undoped channel layer with a material layer above and below the undoped channel layer, the undoped channel layer having a bandgap less than a bandgap of each material layer and each material layer including a planar doping layer, further wherein the heterojunction structure includes a material system including at least one of GaAs, GaN, and InP;
providing a not intentionally doped (NID) layer overlying the heterojunction structure;
providing a heavily doped semiconductor layer overlying the NID layer;
forming a first recess within the heavily doped semiconductor layer, the first recess extending from a source region to a drain region of the microwave field effect transistor;
providing a step gate dielectric overlying the NID layer within the first recess;
providing an interlevel dielectric layer overlying the step gate dielectric;
forming source/drain (S/D) ohmic contacts overlying respective source and drain regions;
forming a top dielectric layer overlying the interlevel dielectric layer and the S/D ohmic contacts;
forming a step gate opening in the top dielectric layer and the interlevel dielectric layer, within the first recess between the source and drain regions;
forming a Schottky gate opening within the step gate opening, the Schottky gate opening extending through the step gate dielectric layer and the NID layer;
providing a barrier metal layer overlying a portion of the heterojunction structure and sidewalls of the NID layer and step gate dielectric within the Schottky gate opening, the barrier, metal layer further overlying the step gate dielectric, the NID layer, a portion of the heterojunction structure, and sidewalls of Interlevel dielectric and top dielectric within the step, gate opening;
and
providing a gate metal overlying the barrier metal layer within the Schottky gate opening and within the step gate opening.

11 more elements

Dependencies are inferred from the claim text.